A wheelchair seat cushion must perform a number of important functions. The seat cushion should be comfortable and capable of providing proper support for optimal posture and posture control for a considerable length of time. The seat cushion should also assist, or at least not materially hinder, the user in maneuvering the wheelchair, permit a useful range of motion from the pelvis and upper torso of the person, and create stability and security for the person within the wheelchair. Perhaps most importantly, the seat cushion should help prevent and reduce the incidence of pressure ulcers created by prolonged sitting on the cushion without adequate pressure relief. Pressure ulcers can become a very serious health problem for individuals who must remain constantly in contact with the support cushion, and it is important to avoid such pressure ulcers.
Wheelchair users like everyone are of substantially different sizes, weights and shapes. Many wheelchair users have physical disabilities and associated posture and postural control impairments such as those typically caused by congenital disorders. Other wheelchair users, such as those who have been disabled by acquired or traumatic injuries, may have a more typical size and shape. In all of these cases, the support contour of the wheelchair seat cushion must safely support the anatomy of the user, whether the anatomy is abnormal or more typical. Wheelchair seat cushions must fit and perform properly to prevent further physical impairment and pressure ulcers. The cushion must also enhance the functional capabilities of the user by supporting independence in activities of daily living. There are a number of different theories or approaches for configuring the support contour of a wheelchair seat cushion to avoid pressure ulcers and to provide adequate postural alignment.
To provide the best individualized support, the cushion must accommodate the anatomical particularities and preferences of the user. Custom wheelchair cushions are used for this purpose. Most custom wheelchair cushions are created from an impression of the anatomy of the user. After capturing a shape of the user's anatomy, the captured shape is used to construct a mold for the cushion. Then the mold is used to fabricate the cushion, including the support contour which interfaces with the user's anatomy from which the shape was originally captured. There are a number of different theories for configuring the support contour to address the perceived needs and requirements of the user.
The most prevalent approach used to configure the support contour of a custom cushion, at least at the time of filing hereof, is to distribute the weight of the user substantially uniformly over the entire support contour. The uniform pressure distribution is theorized to reduce the incidence of pressure ulcers because the uniform pressure distribution is thought to avoid localized high-pressure points which cause pressure ulcers. The substantial conformance of the support contour to the anatomical shape of the user is also believed to encourage the user toward proper postural alignment.
A new support theory is described in the above-identified U.S. patent application Ser. No. 10/628,860. This new support theory is based on offloading and isolating pressure and shear forces from the skin surrounding the bony prominences of the user's pelvic area skeletal structure. Applying this support theory involves configuring the support contour with additional clearance, and therefore achieving greater pressure relief, around the ischial tuberosities, the greater trochantors, the coccyx and the sacrum in the pelvic area, while transferring more support to the broader tissue and musculature below the proximal thigh leg bones and at the posterior lateral buttocks. Pressure and shear forces on the skin around the bony prominences is relieved, and pressure is transferred to the broader tissue areas to encourage proper postural alignment. The pressure transferred to the broader tissue areas encourages proper postural alignment, while making offloading possible.
To execute successfully any of the different support theories, the support contour of the cushion must be created relative to the captured shape of the individual. Otherwise, the user can not be supported adequately to achieve the desired objectives of the support theory.
There are a number of sophisticated methods and devices available for use to determine and capture anatomical shapes. One type of device is a seating simulator. A seating simulator uses a relatively large chair-like structure in which flexible bags or containers of beads are confined. The user is seated on the bags and the beads distribute themselves around the user's anatomy. A vacuum is then applied within the bags, and the exterior pressure on the bags forces the beads to hold the conforming position. The user is then removed, and the user's shape is captured. Any adjustments are thereafter made. To translate the captured shape into information which can be used to create the custom cushion, relatively sophisticated electronic mapping equipment is moved over the shape held by the bag. A multiplicity of different points across the shape are measured, and the measurements are transferred electronically to a software computational algorithm or program which defines a mathematical simulation of the captured shape of the users anatomy. This simulation is thereafter used to create a mold from which the cushion is formed. Alternatively, a plaster or other material casting is made of the captured shaped directly from the bag while the captured shape is held. The casting is shipped to a cushion manufacturer for interpretation and fabrication of a custom cushion having the desired support contour.
Another type of shape-capturing device uses a two-dimensional grid of plungers or rod-like elements which are brought into contact with the users anatomy. The relative displacement or movement of the plungers due to contact with the anatomy is measured. The measurement data is then transferred electronically and is used by a computational algorithm or program which defines a mathematical simulation of the captured shape. Thereafter, the simulation is used to create a mold from which the cushion is formed.
The described types of shape-capturing equipment are sophisticated and relatively expensive to use, and that expense must be charged as part of the price of the custom cushion. The size of the equipment makes it inconvenient for transportation to the user, which can be a problem or at least an inconvenience if the user cannot travel comfortably. At the very least, the practical cost of the cushion is exaggerated by the added travel expenses and inconvenience to the user.
Even though the described types of shape-capturing and shape-simulating equipment may make hundreds or even thousands of measurements at different locations over the anatomy of the individual, those numbers of measurements might still be relatively coarse, particularly in locations where significant changes in contour of the anatomy occur. The computational shape-simulating programs must interpolate the measurements, and that interpolation may not be entirely accurate. As a consequence, the cushion may not be as comfortable or effective as desired.
A more significant problem with the described types of shape-capturing and shape-simulating equipment is that it does not measure a fully-loaded anatomical shape. A fully-loaded shape is one which accurately reflects the effect of the full weight of the individual against a resistance. The resistance will be from the cushion once it is fabricated. In the case of the shape-capturing equipment which uses beads confined in bags, certain limited areas of the entire anatomy will contact the beads with exaggerated loading, while other areas of the entire anatomy will not naturally contact the beads at all. For example, sitting on the bag will transfer virtually the entire weight of the individual from the tissue surrounding the ischial tuberosities to the beads in the bag. Relatively less or little weight will be transferred from the lateral posterior buttocks and sides of the pelvic area to the beads. In order to simulate the shape of these low weight transfer areas, the beads in the bag must be pushed up against the anatomy. However, pushing the beads against the anatomy does not result in the same shape as would occur from a fully loaded condition in which the weight of the individual is fully and naturally resisted over the entire contact area. The combination of areas of exaggerated loading and simulated loading creates distortion in the captured shape as compared to a fully loaded shape, and this distortion may be reflected by insufficiencies in the support from the cushion.
In the type of shape-capturing equipment which utilizes a grid of plungers, resilient foam or spring-like devices surround each plunger. The resiliency of the foam or springs is intended to create resistance to the weight of the anatomy, thereby allowing the user to sit down on or recline against the plungers. However, the foam or springs do not uniformly load the anatomy. Those portions of the anatomy which depress the plungers to a greater extent will be resisted by greater pressure compared to the resistance from plungers contacting other areas of the anatomy which are less depressed. The amount of resistance increases with an increase in the distance traveled by the plunger. The shape captured from such devices is therefore a non-uniformly loaded shape, in the sense that the resistance is not uniform over the entire area of the anatomy. A cushion formed from a nonuniformly loaded shape may be inadequate.
Another problem with shape-capturing equipment is that the captured shape is based on a static position and posture of the user. For the equipment to capture the image accurately, the user must remain still. In actual use, the user is almost always moving on the cushion. For example, the user is rocking his or her upper torso when turning the wheels of the wheelchair. The user may be leaning from one side to the other when reaching or may be leaning forward to work at a desk. A support contour which is configured from a static anatomical shape is prone to create pressures and shear forces at bony prominences, resulting in an increased risk of pressure ulcers, due to the natural movement of the user.
Because of the necessity to use shape-capturing equipment and because the user must stay stationary while the shape is captured in such equipment, a wheelchair user is not able to test and evaluate the support contour of the cushion before it is formed. The ability of the cushion to protect the skin, to assist the user in manipulating the wheelchair, or at least not to inhibit the user in maneuvering the wheelchair are important aspects of the cushion. If the cushion positions the user too far forward, or too far rearward, or too low or high, the center of gravity within the wheelchair and the ability to maneuver the wheelchair and comfort and safety of the user can be impaired. However, these actual-use aspects of the cushion are only determinable after the cushion has been fabricated.